Control circuit



Patented Nov. 2, 1937 UNITED STATES,

PATE i QPF-lm l maar:

16 Claims. (ci. 1784-44) This invention relates to signal transmission systems and particularly to circuits for controlling the energy of signals on transmission systems. v

One object of the invention is to provide la signal transmission system with control circuits for adjusting the gain on a line in an improved manner to maintain the volume substantially constant.

Another object of the invention is to provide a signal transmission line with control circuits that shall control a potentiometer to raise and to lower the gain on the line at different rates and maintain the volume on the line substantially constant. Another object of the invention is to provide a signal transmission line with control circuits that shall control two potentiometers for raising and lowering the gain on the line to reduce the range of volume on the line. Y

Another object of the invention is to provide a signal transmission line with control circuits that shall control two potentiometers for raising and lowering the gain on the line to increase the range of volume on the line. 25 A further object of the invention is to provide a four-wire transmission line having a potentiometer in the east line and in the west line with control circuits that shall operate the potentiometers in the east and the west lines op- 30 positively according to the volume of the signals on one of the lines and that shall raise and lower the gain in each line at different rates. Y

In signal transmission systems it is desirable to control the volume of transmitted signals inV until the volume of the signals received over the line is above the peaks of the weakest talker.

If the volume of the signals on the line beyond 50 the amplifier is below a predetermined lower limit, the potentiometer is operated to raise the gain and if the volume of the signals on the line beyond the amplifier is above a predetermined upper limit, the potentiometer is operated to lower 55 the volume of the signals.

In a four-wire circuit constructed Vin accordance with the invention.twopotentiometers which are respectively placed in the east line and the l west Aline of the four-wire. circuit are controlled by two magnetic clutch' mechanisms. The magnetic clutch mechanisms are rotated by a constantly-rotatingvmotor.V vThe clutch mechanism which is adapted to operate a potentiometer in one line, for example, the east line, to raise the gain, is operated at'a relatively slow speed.,l whereas theY other clutch mechanism which serves to lower the gain in the east line is operatedata `relatively highfspee'd; The two rpotentiometersV are connected to the east and. the Vwest'lines to -f east line beyond -the potentiometer and the ainpli-v Y lier controls a gain' decreaser relay and a gain increaser'disabler relay. If the peaks of speech waves on the east line beforefthe potentiometer weakest talker andthevolumebeyond Ythe potentiometer and amplier in the east line is below a predetermined lower limit, one of the clutch: mechanismsA is controlled to operate the Vtwo potentiometers so asto vraisethe gain in the east line andY lower the gain in -the west line. When the volume-of the signals beyond the potentiometer and amplier in the east line is raised above the predetermined :lower limit, the'clutch L and the amplifier are above theY peaks ofY the Y mechanism which serves to raise the gain in the east line is released. If the volumeon-the east line beyond the potentiometer and. amplier is above a predetermined upper limit, the second clutch mechanism is controlled to operate thetwo potentiometers so asV to lower the gain in the east line and raise the gain in the west line. A

magnetic brake is provided for quickly stopping .the operation of the potentiometers when eitherV of the clutch mechanisms is released.

In the accompanying drawings:

Figure 1 is a diagrammatic viewof gain control circuits constructed inaccordance with the invention;

FigL-.Z is a diagrammatic view of a modification of the control circuits shown in Fig. 1, wherein the volume ofthe signals on the transmission line maybe compressed any desired per cent; y

Fig. 3 a diagrammatic view of a modification of the control circuits shown in Fig.1, wherein the volume of the signals on the transmission line may be expanded any desired per cent; and

Figs. fi and 5 are diagrammatic viewsof modifications of the circuits shown in Figs. 2 and 3.

Referring to Fig. 1 of the drawings, a four-wire circuit comprising an east line I and a West line 2 is controlled to maintain the volume on the east line substantially constant. An amplifier 3 of any suitable type is provided in the east line I and an amplifier 4 is provided in the west line 2.

provided in the east line I ahead of the amplier 3 and a potentiometer 'I having a control arm 8 is provided in the west line 2 ahead of the'am-L plier 3. The potentiometer arms Gand 8 are mounted on a shaft ilI which is controlled by the clutch mechanisms I 8 and II. Rotation of` the potentiometer arms E and 8 in a clockwise direction, as viewed in Fig. l of the drawings, serves to increase the gain on the east line 'and decrease the gain on the west line. Rotation of the arms 8 and 8 in a counter-clockwise direction serves to decrease the gain on the east line and increase the gain on the west line.

The clutch mechanism I8 which serves to'rotate the potentiometer arms` 6 and 8 in a clockwise direction comprises arclutch magnet lila having the terminals thereof connected to slip rings I2 and a gear wheel 22. The clutch magnet la, the slip rings I2 and gear wheel 22 are rotatably mounted on the shaft 8. A disc lf3 which is Xedly mounted on the shaft 9 is engaged by the electromagnet Ida when energized to connect the shaft 9 to the gear wheel 22.v The gear wheel 22 is connected to a gear wheel 23 on a shaft I'. The shaft H is connected by worm gearing I8 to a constantly rotating motor I3. The motor I9 effects constant rotation of the electromagnet 'I 8a and upon energization of the electromagnet effects rotation of the shaft 9 and the potentiometer arms 6 and 8. Y

The clutch mechanism II comprises electromagnet 28 having the terminals thereof connected to slip rings 2l. The electromagnet 20, the slip rings 2| and a gear wheel I3 are rotatably mounted on the shaft 9. The gear wheel i 3 meshes with a pinion I5 with a gear wheel IS mounted on the shaft II. The motor I9 by means of the worm gearing I8, shaft Il and gear wheels I5 and I 3 rotates the electromagnet 23 constantly in a direction opposite to the direction of rotation of the electromagnet l 8a' by the motor I 9. A magnetic'disc 24 is fxedly mounted on the shaft 9 adjacent to the electromagnet 20. Upon energization of the electromagnet 28, the magnetic disc 25 is connected to the electrcmagnet so that the disc 2li and shaft-9 having the potentiometer arms 6 and 8 mounted thereon are rotated in accordance with the rotation of the electromagnet. In the above construction it will be noted the potentiometer arms 6 and 3 when controlled by the electromagnet 26 are operated at a fast-er rate than when controlled by the electroinagnet I 3a.

Y A control arm 25 is mounted on the shaft 9 for controlling two limit switches 23 and 2l. When the arm E of the potentiometer 5 has been operated to its extreme position for increasing the gain on the east line, the limit switch 2'! is-opened by the arm 25. When the potentiometer 5 has reached its extreme lower position for decreasing the gain on the line, the limit switch 23 is opened by the arm 2E. A stationary brake electromagnet 23 is positioned adjacent to a magnetic disc 29 which is flxedly mounted on the shaft 9. Upon energization of the brake magnet 28 the disc 29 is engaged to effect a relatively quick stopping of the rotation of the shaft 9.

A gain increaser relay 30 is provided for completing a circuit through the clutch electromagnet Illa and a gain increase disabler relay 3i is provided for controlling a relay 32 to open the circuit of the clutch electromagnet Ia when the volume of the signals on the east line beyond the y :amplier 3 is above a predetermined lower limit. A potentiometer 5 having a control arm Ii is A gain decreaser relay 33 is provided for completinga circuit through the clutch elcctrornagnet 20 when the volume of the signals on the east `lline beyond the amplifier 3 is above a predetermined upper limit. VThe gain increaser relay 353 is controlled by a forward-acting circuit 34 and l' the gain `decreaser relay 33 and the gain increase disabler. relay 3| are controlled by a backwardacting control circuit 35. The forward-acting control circuit '3e comprises two space discharge amplifier tubes 35 and 3.1 anda diode-triode tube 38. The input circuit of the ampliiier 33 is connected to the east line I before a transformer 38 by means of transformer 40. Condensers 4I and resistance elements 42 are inserted in the connection between the transformer i3 and the east -line I. The output circuit of amplifier 36 is connected to the input circuit of the amplier 3'I by means of a transformer 43. The output circuit of the amplifier 3'! is connected by, a transformer 44 to the diode portion of the tube 38. A mid-tap from the secondary Winding of the transformer fr!! is connected to the grid of the tube 38 and to the cathode of the tube 33 through a capacity element 45 and resistance element 4S. The capacity element 35 and the resistance element It are connected in parallel to each other. The plate cathode circuit of the triode portion of the tube 38 is connectedin series with the gain increaser relay 33 and a plate battery 4i. Battery 48 is provided for heating the 'filaments of tubes 38, 3'! and A battery 49 is provided for supplying plate potential to the tubes 3E and 3l. Condensers 53 serve as blocking condensers. The resistance elements 5I and A52 connect the grids of he tubes 36 and 31 to points effectively negative with respect Vto the ycathodes of the tubes 33 and 31. The resistance elements 5I and 52 in combination with the condensers 58 lter out disturbances in the filament battery 43 to provide a constant effective grid bias.

Normally, the gain increaser relay 38 is operatedby the current from the battery 4'! flowing through the triode portion of the tube 38. When the relay 38 is operated, the circuit of the clutch electromagnet Ia. is held open. When the signals on the east line I are above the peaks of the weakest talker, the -diode portion of the tube 38 rectifies sufficient current for impressing a `negative bias-on the grid of the triode portion of the tub-e 38 to release the relay 38. The two electrodes of the diode portion of the tube 38 are respectively` connected to the terminals of the secondary winding of the transformer 44. The mid-tap of the secondary winding of the transformer 44 is connected through the capacity 45 in parallel with the resistance 4S to the cathode of the tube 33. `In such connection, potential is built up on the capacity 45 for impressing negative bias on the grid of the ktriode portion of the tube 38. When the negative bias on the grid of the tube 38 is raised to a predetermined point, the space current ow through the triode portion of the tube 38 isY reduced toa point for releasing the relay 30. The relay 30 is released when the voltage on the line before the transformer 39 is above the peaks of the weakest talker.'

` The backward-acting circuit 35 comprises an amplifier space discharge tube 53 and a diodetriode space discharge device 54. The input circuit of the amplifier tube 53 is connected by a transformer 55 to the east line I beyond the amplifier 3. The output circuit of the amplifier 53 is connected'by a transformer 56 to the diode portion of the diode-triode tube 54. The output terminals of the secondary winding of the transformer 56 are connected to the electrodes of the diode portion of the tube 54. A central tap from the secondary winding of the transformer 56 is connected to the grid of the triode portion of the Ytube 54 and to the cathode of the tube 54 through a resistance element 51 and a capacity element 58. The diode-triode tube 54 is controlled by the signals beyond the amplifier 3 on the east line I in the same manner -as the tube 38 is controlled by the signals on the east line I before the transformer 39. A battery 59 is provided for supplying plate potential to the triode portion of the tube 54. The winding of the gain decreaser relay 33 is connected in the plate circuit of the tube 54 in parallel with a winding of the gain increase disabler relay 3|. A resistance element 66 is included in series with the winding of the gain increase disabler relay 3I. A battery 6I supplies plate potential to the amplifier 53 and a battery 62a. supplies heating current to the laments of the tubes 53 Vand 54. Condensers 62 serve as blocking condensers, The resistance element 63 connects the grid of the tube 53 to a point eectively negative with respect to the cathode of the tube 53. The resistance element 63 in combination with the condenser 62 filters out disturbances in the filament battery 62a to provide a constant effective grid bias.

If the voltage on the east line I before the transformer 39 is above the peaks of the weakest talker and the volume on the east line beyond the amplifier 3 is below a predetermined lower limit, therelay 39 will be released by the forwardacting control circuit 34. The gain decreaser relay 33 and the gain increase disabler relay 3l are held in operative position by means of the backward-acting circuit 35 and the relay 32 is held in released position as shown in the drawings by the gain increase disabler relay 3l. A circuit is completed by release of the relay 36 for Voperating the electromagnet I9a which may be traced from battery 65 through a resistance element 65, armature of the gain decreaser relay 33 in operative position, armature of the gain increaser relay 30 in released position, slip rings I2, electromagnet Illa, limit switch 2?, armature ofthe relay 32 in released position and ground return to the battery 65. The clutch magnet lila attracts the disc I4 and by means of the motor I9, effects rotation of the potentiometer arms 6 and 8 in a clockwise direction as shown on Fig. `lof the drawings to increase the gain on the east line I and decrease the gain on the west line 2. 'Ihe gearing comprising gears 22 and 23 serves to eiect raising of the gain at a relatively slow rate.

When the volume on the east line I beyond the amplifier 3 is raised above the predetermined .lower limit, the gain increase disabler relay 3| is released to effect operation of the relay 32. The relay`32 upon operation breaks the energizing circuit for the clutch electromagnet Illa to prevent any further increase in the gain on the east line I. The gain increase disabler relay V3| is provided with two windings 61 and 68 and the relay 32 is provided with two windings 69 and 16. When the relay 3| is in operative position, winding 69 is connected to two opposing batteries 1I and 12 so that no operation of the relay 32 can take pl-ace. Upon release of the relay 3|., the battery 12 is disconnected from the winding 69 of the relay 32 so that the relay 32 is operated by the battery 1I through a circuit including a resistance element 13. When the armature of the gain increase dis-abler relay 3| engages its back contact, a circuit is completed through resistance elements 14 and 15 for energizing the winding 15 of the relay 32 from the batteries 12 and 16. A condenser 11 is charged to effect a hangover in the operation of the relay 32 when the gain increase disabler relay 3l is again operated. A circuit is cuit of the clutch electromagnet ma is shimted v by a condenser 11 and a rectifier 18. During thev operation of the clutch electromagnet Ia., con? denser 11 is charged and upon opening of the circuit through the clutch electromagnet Illa the charge on'the condenser'11 is discharged through a rectifier 19for energizing the brake electromagnet 28. The brake electromagnet 28, uponA energization, engagesthe disc 29 on the shaft 3 for effecting a relatively quick stopping of the rotatable elementr of the potentiometer arms 6 and 8.

When the volume on the east line I beyond the amplifier 3 is above a predetermined upper limit,

the gain decreaser relay 33 is released by the backward-acting control circuit 35. Upon re` lease of the relay 33, a circuit is completed for energizing the clutch velectromagnet 2li. The circuit for energizing the clutch electromagnet Y2liY may be traced from the grounded battery 65 through the resistance element 66, armature of the relay 33 in released position, lamp 33, slip rings 2l and electromagnet 29,*limit switch 25 and ground return to the battery 65. The clutch electromagnet 20 upon operation attracts the disc 24 for effecting rotationfof the shaft 9 and the potentiometer arms 6 'and 8 in a counter-clockwise direction. Counter-clockwise rotation of the potentiometer rarms 6' and 8 serves to decrease the gain on the east line I and to increase the gain on the west line 2. A lamp 83 is in#V` eluded in the circuit of the electromagnet@ in order to indicate when the electromagnet is in operation. A similar lamp 8l is provided in the circuit of the clutch electromagnet Illu..

When the volume on the east line i beyond y amplifier 3 is reduced below the predetermined upper limit, thegain decreaser relay 33 is operated by the backwardlacting control circuit 35 to open the circuit of the clutch electromagnet 20 and prevent further decrease in vthe gain on the east line and increase in the gain on the west line. At this time the charge on the condenser 11 energizes the brake electromagnet 28 to eifect quick stopping of the rotative movement of thepotenloss effected by the potentiometer IOI.

tiometer arms I3 and 8. If the volume on the east line I beyond the amplifier 3 falls below the predetermined lower limit, the gain increase disabler relay 3| is released to again effect operation of the clutch electromagnet |a. The operation of potentiometer arms 6 and 8 by the clutch electromagnet Illa has been described heretofore. The gain increase disabler relay 3| is made more sensitive than the gain decreaser relay 33 in order to effect operation of the relays at different volume levels.

Referring to Fig. 2 of the drawings, a modification of the invention is shown wherein the volume of the signals on the line may be compressed any desired per cent. A signal line |09 has a potentiometer IOI connected across it and an amplifier |02 is positioned on the line beyond the potentiometer. A branch line |03 is connected to the transmission line' |00 beyond the amplifier |02 and a potentiometer |04 is connected across the branch line. The two potentiometers I 0| and |04 are provided with control arms and |06 which are governed in the same manner as the control arms 5 and 8 shown in Fig. 1 of the drawings. The changes in decibel loss effected by the two potentiometers |0| and |04 vary in accordance with the compression in volume that is desired on the transmission line beyond the amplifier |02. If the volume of the signals on the transmission line beyond the amplifier 02 is to be compressed one-half with respect to the volume of the signals before the potentiometer IOI, then the change in loss effect by the potentiometer |04 is made the same as the change in A backward-acting control circuit 35 is connected to the branch line |03 beyond the potentiometer |04 for controlling the movement of the potentiometer arms |05 and |05 in the same manner as the backward-acting control circuit 35 in Fig. 1 of the drawings controls the operation of the potentiometer arms 6 and 8. A forward-acting control circuit 34 which is similar to the forwardacting control circuit 34 shown in Fig. 1 of the drawings is provided for preventing any control of the potentiometer arms |05 and |05 until the peaks of the speech on the line |00 before the potentiometer I 0I are above those of the weakest talker. The backward-acting control circuit 35, the forward-acting control circuit 34 and the clutch mechanisms and control circuits 99 governed thereby are similar in construction and operation to the same parts shown in Fig. 1 of the drawings. Accordingly, a detailed description of the operation of these parts with respect to Fig.

2 is deemed unnecessary.

If the volume of the signals on the transmission line before the potentiometer is above the volume of the weakest talker, then the control circuit 35 operates to maintain constant volume on the branch line |03 beyond the potentiometer |04. When constant volume is maintained on the branch line beyond the potentiometer |04, it will be noted that the volume range of the signals on the transmission line I0| beyond the amplifier |02 will be compressed onehalf. This circuit operates somewhat in the manner of the circuit disclosed in the patent to S. Dob-a, No. 1,854,828 dated April 19, 1932. It will be noted that if the potentiometer arms |55 and |06 are both rotated in a clockwise direction, the gain on the transmission line and the branch line will be increased and that if each of the potentiometer arms |05 and |06 are rotated in a counter-clockwise direction, the gain on the transmission line and the branch line would be decreased.

Referring to Fig. 3 of the drawings, control circuits are shown for expanding the signals on the line any desired per cent. In Fig. 3 of the drawings, two potentiometers |01 and |08 are connected in tandem across the transmission line |09 and are separated by an amplifier ||0 of any desired type. The potentiometers |01 and |08 are respectively provided with contact arms and I i2 and are so connected to the transmission line that rotation of the contact arms III and ||2 in a clockwise direction will increase the gain effected by the potentiometer |01 and decrease the gain effected by the potentiometer |08. A11 opposite effect takes place if the two potentiometer arms III and I|2 are rotated in a counterclockwise direction. The changes in decibel loss effected by the two potentiometers |01 and |08 are varied in accordance With the expansion of the signals which is desired. If the volume of the signals on the transmission line |09 beyond the potentiometer |08 is to be double the volume of the signals on the line |09 before the potentiometer |01, then the change in decibel loss effected by the potentiometer |08 is double the change in decibel loss effected by the potentiometer 01. The impedance values of the two potentiometers |01 and |08 are varied in accordance with the expansion desired of the signals on the transmission line |09 beyond the potentiometer |08 with respect to the signals on the transmission line |09 before the potentiometer |01.

A forward-acting control circuit 34 which is similar in construction and operation to the control circuit 34 as shown in Figs. 1 and 2 of the drawings is provided for preventing any operation of the potentiometer arms III and II2 until the volume of the signals on the line |09 before the potentiometer |01 is above that of the weakest talker. A backward-acting control circuit 35 similarin construction and in operation to the backward-acting control circuit shown in Figs. 1 and 2 of the drawings is provided for controlling the operation of the potentiometer arms II and ||2. The control circuits 34 and 35 govern clutches and control circuits 99 in the same manner as the potentiometer arms 6 and 8 are controlled by the clutch mechanisms shown in Fig. 1 of the drawings.

The backward-acting control circuit 35 is connected to the transmission line |09 between the amplifier H0 and the potentiometer |08. When the backward-acting control circuit 35 is so connected, it will be noted that constant volume is maintained on the line |09 between the amplifier l0 andthe potentiometer |08, and the volume of the signals on the line 09 beyond the potentiometer m8 will be expanded according to the difference in the changes in decibel loss effected by the potentiometers |01 and I 08. If the impedance value of the potentiometer |08 is double the impedance value of the potentiometer |01, the vol,- ume of the signals beyond the potentiometer |08 will be doubled with respect to the volume of the signals on the line I 09 before the potentiometer |01.

Referring to Fig. 4 of the drawings, a range reducer or compressor is shown which operates in a manner similar to the compressor shown in Fig. 2 of the drawings. A potentiometer IIS is connected across the transmission line I5 and a potentiometer ||1 is connected across a branch line |3. The branch line I I8 is connected to the transmission line I I5 at a point before the poten- 'z5 1 of the drawings,.is connected to the transmis-1l tiometer H6. An amplifier 9 of any suitable type is connected to the transmission line ||5 at a point beyond the potentiometer ||6. 'I'he two potentiometers H5 and are respectively provided with contact arms |25 and |2|. The potentiometer I |6 is so connected across the transmission line H5 and the potentiometer is so connected across the branch line ||8 that if the Contact arms |20 and |2| are rotated in a clockwise direction, the gain on both the transmission line and the branch line will be increased. An opposite eiect takes place if the two contact arms |20 and I 2| are rotated in a counter-clockwise direction. A forward-acting control circuit 34 is connected to the transmission line |5 before the connection of the potentiometer ||6 across the transmission line for preventing any control of the potentiometers until the volume on the transmission line before the potentiometer I6 is .above that of the weakest talker.

The control circuit 34 in Fig. 4 of thedrawings is similar in construction and operation to the control circuit 34 shown in Fig. l of the drawings. A-backward-acting control circuit 35 is connected to the branch line ||8 beyond the potentiometer The control circuits 34 and 35 govern clutches and control circuits 99 for operating arms |20 and |2| in the same manner as the potentiometer contact arms 6 and 8 in Fig. 1 of the drawings are governed. The changes in decibel loss effected by the potentiometers ||6 and are varied according to the compression desired on the transmission line 5 beyond the amplifier |9. If the signals beyond the potentiometer ||6 are to be compressed one-half with respect to the signals before the potentiometer, then the changes in decibel loss effected by the potentiometer i is twice the change in decibel loss effected by the potentiometer ||6. In such an arrangement the potentiometer is so operated as to maintain constant volume on the branch line I8 beyond the potentiometer While the potentiometer contact arm |2| is being operated toV maintain constant volume on the branch line, the potentiometer arm |20 is being operated to compress thesignals on the transmission line ||5 one-half.

Referring to Fig. 5 of the drawings, a range expander is shown which operates in a manner similar to the range expander shown in Fig. 3 of the drawings. nected across a transmission line |24 and a potentiometer |25 is connected across a branch line |26. The branch line |26 is connected to the transmission line' |24 at a point before the connection of the potentiometer |23 to the transmis sion line. An amplifier |21 is connected to the transmission line |24 at a point beyond the potentiometer |23. The potentiometer |23 is provided with a contact arm |28 and the potentiometer 25 is provided with a contact arm |29. The potentiometer |23'effects a larger change in decibel loss than the change in decibel losseffected by the potentiometer |25. Furthermore, the potentiometers |23 and 25 are operated in opposite directions. If the contact arms |28 and |29 are operated in a clockwise direction, the gain effected by the potentiometer |23 is increased and the gain on the branch circuit |26 is decreased by the potentiometer |25. An opposite effect takes place if the contact arms |28 and |29 are rotated in a counter-clockwise direction.

i A control circuit 34, similar in construction and operation to the control circuit 34 shown in Fig.

A potentiometer |23 is con-f sion line |24 at a point before the potentiometer |23 for .preventing operation of the contact arms |28 and |29 until the volume on the transmission line |24 before potentiometer |23 is above that of the weakest talker. A control circuit '35 is connected tothe branch circuit |26 at a point beyond the potentiometer |25. The control circuits'34 and4 35 govern clutches and.r control circuits 99 foroperating the potentiometer arms |28 and |29 in the same manner as the potentiometer arms 6 andV 8 in Fig. 1 of the drawings are gov-,- eriied. The potentiometer |25 is so operated as to maintain constant volume on the branch line |26 beyond the potentiometer |25.v At the same time the potentiometer |23 is operated to expand the volume of the' signals of the transmission line |24. If the changes in decibel loss effected by the potentiometer |23 are twice the changes in decibel losseffected `by the potentiometer |25, ther range of the signals beyond the potentiometer |23 will be double that of the range of the signals on the transmission line |24 before thepotentiometerl Modifications inthe circuits and in the ari rangement and location of parts may be made within the spirit and scope of the invention and Y gain'of said amplifier, and means controlled ac-` cording to the volume 'of the signals on'the line for. operating said contact arm at one fixed rate to'raise the volume and for operating said contact arm at another fixed rate to lower the volume.

2. In gain adjusting circuits for a transmission line, a potentiometer having an adjustable contact arm for controlling the gain on the transmission line, means operated when the volume onv the line beyond said potentiometeris below a predetermined limit for operatingsaid contact arm at one fixed rate to raise the volume on the line and means operated when the volumeron the line beyond said potentiometer is above a predetermined level for operating said contact arm at a different fixed rate to lower the volume on the. line. i

' 3. In gain adjusting circuits for a transmission Y line, an amplifier on said line, a potentiometer having a movable contact arm for controlling the gain of said amplifier, means operated when the volume of the signals on the line beyond said amplifierfalls below a predetermined lower limit for operating said arm at a relatively slow rate. to raise the volume of the signals and means operated when the volume of the signals on the line beyond said amplifier rises above a predetermined 'upper limit for operating said armv at a relatively fast rate to lower the volume of the signals. Y

4. In a signal system, a transmission line, an amplifier on said transmission line, a potentiometer having a movable contact arm for controlling the-gain effected by said amplifier, means comprising clutch mechanism operated when the volume of the signal on the line before the potentiometer is above the volume of the weakest talker and the volume on the line beyond said amplifier is below a predetermined lower volume limit for operating said arm at a relatively vslow rate toY raise the volume and Vmeans comprising clutch mechanism operated when the volume of the signalsl on the line beyond said amplifier is above a` predetermined upper limit for operating said arm at a relatively fast rate to lower the signal volume.

5. In a signal system, a four-wire. circuit having a receiving line and a transmitting line, an amplier and a potentiometer having a controlling arm in each of said lines, means' comprising clutch mechanism controlled in accordance with the signal volume on the transmitting line beyond the potentiometer and amplier therein for operating the arms of said potentiometers to vary the two potentiometeis oppositely and means for preventing operation of the clutch mechanism in a direction to raise the gain on the transmitting line when the volume of the signals on the transmitting line before the potentiometer therein is below the peaks of the weakest talker.

6. In a signal system, a four-wire circuit having a receiving line and a transmitting line, an amplifier and a potentiometer having a controlling arm in each of said lines, means comprising clutch` mechanism for operating the arm of the potentiometer in the transmitting line to raise the gain and for operating the arm of the potentiometer in the receiving line to lower the. gain when the volume of the signals on the transmitting line before the potentiometer and amplier therein is above the volume of the weakest talker and the signal volume on the transmitting line beyond the potentiometer and amplier is below a predetermined lower limit, and means comprising clutch mechanism for operating the arm of the potentiometer in the transmitting line to lower the gain and for operating. the arm of the potentiometer in the receiving line to raise the gain when the volume of the signals onA the transmitting line beyond the-potentiometer and amplifier therein raises above a predetermined upper limit.

7. In a signal system, a transmission line, an ani-plier onsaid line, a potentiometer having a movable contact arm for controlling the gain eected by said ampliiier, gain raise clutch mechanismV for controlling saidicontact arm to raise the gain on the line at one rate, gain lower clutch mechanism for controllingl said contact arm to lower the gain on the line: at a diierent rate, means for selectively operating said clutch mechanisms according to the energy volume on the line beyond the potentiometer and amplifier to maintain the volume on the linesubstantially constant.

8. Ina signal system, a transmission line, an amplier on said line, a potentiometer having a movable contact arm for controlling the. gain effected by said amplifier, gainV raise clutch mechanism. for controlling said. arm to raise the gain effected by said ampliiier, gain lower clutch mechanism for controlling said arm to lower the gain effected byy said amplifier, means operated when the volume on the line beyond said amplifier falls below a predetermined lower limit for operating said gain raise clutch mechanism to raise the volume on the line beyond the amplifier, means operated when the volume on the line beyond the amplifier rises above a predetermined upper limit for operating said gain lower clutch mechanism to lower the volume on the line beyond-'the amplifier, and breaking means operated upon return of the volume on the line to normal value between the upper and lower limits and release of the clutch mechanisms for quickly stopping niovementof the contact arm.

9. In gain adjusting circuits for a transmission line, a constantly operating motor, two electromagnetic clutches each having one member adapted to. be rotated by said motor, another"` member normally stationary and adapted tor be connected to the rotating member, and an electromagnet for connecting the two' members together when energized, gearing for connecting the. two rotating clutch members to the motor to effect rotation at different speeds, a potentiometer having a contact `arm controlled by said normally stationary clutch members, means operative when the volume on the line beyond. said potentiometer is below a predetermined lower level for energizing one of said clutch magnets to operate the Contact arm and raise the gain, and means operative when the volume on the line beyond said potentiometer is above a predetermined upper level for energizing the other clutch magnet to operateV the contact arm and lower thegain.

10'.. In a signal system, a transmission line, an amplier on said line, a. potentiometer having a movable contact arm for controlling the gain effected by saidamplifien' a circuit comprising a diode triode tube connected to said line before said potentiometer and ampliier, means for supplying negative bias to the grid of said tube by the diode portion thereof connected to said circuit, a gain increase relay connected to the output circuit of said tube and normally operated' by the space current flow through said tube, and means controlled by said relay for operating said contact arm to increase the gain effectedby said amplier when the volume on the line before theI potentiometer and; amplier is', above the volume of the weakest talkerand the volume on the line beyond the potentiometer and amplier is below a predetermined lower limit.

1l. In a signal system, a transmission line, an amplier onr said line, a potentiometer having a movable contact arm. for controlling the gain effected by said amplifier, a circuit comprising a diode triode tube connected to said line beyond' said potentiometer and amplifier, means.` for supplying, negative biasV to the grid of said tube by the diodev portion thereof connected to said circuit,ka gain decreaser relay connected: to. the plate and filament circuit' of the triode portion of said tube and normally operated by the space current iiowfthrough. thel tube, and means. controlled by s a-idrelayior operating said'contactlarm to lower the'gain` effected byy saidy amplier when the volumegon the line beyondlt said potentiometer and the ampliiier'rises;` above a predetermined upper limit.

112.` In a signallsystem, aV transmission line, an amplier on said line, a potentiometer having a movable contact arml for controlling the gain effected by saidA amplifier, a circuit comprising a diode triode tube connected to said line before saidpotentiometer and amplifier, means for supplying; negative bias to the. grid of said tube by the diode portion thereof 'connected' to' said circuit, a gain increaserrelay connectedto the output circuit of saidVY tube and normally operated by the space current flow through the tube, a. second circuit comprising a second diode triode tube connected to said line beyond said potentiometer and amplifier, means for supplying negative biasto the grid. of lthe secondv tube by the diode portion thereof connected to the second circuit', a gain decreaser relay and a gainincrease disabler relay connected tothe.- plate and lament circuit of the. triode portion of said second tube and each; normally operated bythe space .current flow through the second tube, means controlled by said gain increaser relay for operating said contact arm to increase the gain eected by said amplifier when the volume on the line before the potentiometer and the amplier is above the volume of the weakest talker and the volume on the line beyond the potentiometer and the amplier is below a predetermined lower limit, means controlled by said gain increase disabler relay for preventing increase of the volume on the line under control of the gain increaser relay when the volume on the line beyond the potentiometer and amplier rises above a predetermined lower limit, and means controlled by said gain decreaser relay for operating said contact arm to lower the gain effected by said ainplier when the volume on Vthe line beyond said potentiometer and amplier rises above a predetermined upper limit.

13. In control circuits for a signal transmission line, a branch line directly connected to the transmission line to receive signals transmitted over the transmission line, two potentiometers respectively connected across the branch line and the transmission line and each having a movable contact arm, and means controlled ac cording to the volume of the signals beyond the potentiometer connected across the branch line which are received from the transmission line for controlling the two potentiometer arms -to vary the volume of the signals on the transmission line beyond the potentiometer therein with respect to the volume of the signals on the transmission line before the potentiometer therein.

14. In control circuits for compressing the volume of the signals on a transmission line, a potentiometer connected across said line and having a movable contact arm, a branch line directly connected to the transmission line to receive signals transmitted over the transmission line, a second potentiometer connected across said branch line and having a movable contact arm, and means controlled according to the volume of the signals on the branch line beyond the potentiometer therein which are received from the transmission line for operating said potentiometer arms to compress the volume of the signal on the transmission line beyond the potentiometer therein with respect to the volume of the signals on the transmission line before the potentiometer therein.

l5. In control circuits for a transmission line, two potentiometers connected across said lineV and each having a control arm, said potentiometer effecting different Vchanges in loss and the potentiometers being so connected to the line that the changes in loss effected by them are Varied'oppositely when the contact `arms are moved in the same direction, and means controlled according to the volume of the signals on the line between said potentiometers for controlling said potentiometers to expand the volume of the signals on the line beyond said potentiometers according to a fixed ratio with respect to the volume of the signals on the line before the i cording to the volume of the signals onthe line between said potentiometers for Vcontrolling said potentiometer arms to expand the volume of the signals on the line 'beyond said potentiometers. HAROLD L. BARNEY. 

